1. Field of the Invention
The present invention generally relates to production of gas and oil using plunger lift technology and, more particularly, is concerned with a valve system for proportioning and controlling flow in a gas sales line of a gas-producing well.
2. Description of the Prior Art
Many gas and oil wells employ a gas flow control valve, known as a "motor valve", that is opened or closed to respectively allow production from or shut-in of the well. The flow control valve commonly used is one that is spring biased to normally assumes a closed condition and requires a supply of external pressurized air above a predetermined level, such as 35 psi, to pneumatically cause opening of the flow control valve against the spring bias. Once the flow control valve is opened, any further supply of external pressurized air to the flow control valve can be cutoff, since the pressurized air already supplied to pneumatically actuate the flow control valve will be retained in it and hold it in the opened condition. To close the flow control valve, the pressurized air retained therein merely is vented off to the atmosphere.
In order to maximize product sales income from a well, it desirable to limit the flow of gas and oil from the well to a sales line to below a maximum operational setting at which a charting device (connected to the sales line records the flow pressure through the line over time. Frequently when a well is first opened by the flow control valve, a spike or surge in the flow pressure is experienced over a short period of time. This surge typically goes well above the maximum operational setting at which the charting device is capable of recording flow pressure. When the maximum setting is exceeded this is referred to in the industry as going "off the chart". The gas and oil producer is not paid for the portion of the product that enters the sales line at a flow pressure that is "off the chart". This quantity of gas and oil can be viewed as an "off the chart" giveaway by the well producer to the gas and oil company purchasing the production. Also, in order to maximize product sales income from a well, it desirable to regulate the velocity of flow of gas and oil from the well so that a separator downstream of the flow control valve can function properly to separate oil from the gas and thereby prevent oil from being suspended and carried with the gas to the sales line and, in effect, given away free to the gas company buying only the gas from the well.
To eliminate "off the chart" and suspended oil giveaways the flow pressure and velocity of the gas and oil must at all times be controlled and regulated so that it will not exceed the maximum operational setting of the charting device and not prevent the separator from performing its intended function. One way to do this is to control and regulate the actuation of the flow control valve from the closed to opened condition. There are proportioning valves on the market which can be used to accomplish this, that is, by controlling the supply pressure to the flow control valve so that it is only opened a desired "percentage" instead of fully open. The flow pressure through the flow control valve will be proportional to the "percentage" open of the flow control valve.
However, problems exist with respect to all prior art commercially-available proportioning valves. They are complex devices, high in price, and require more electrical power to operate than is available from the photovoltaic cells and batteries typically utilized at remote wellhead sites. Thus, none of the commercial-available proportioning valves are economically feasible to use for this application. A high-low controller costing around a thousand dollars is typically purchased by the well producer and employed at the well site as a safety shut-down and turn-on device connected to the flow control valve to prevent the flow pressure from exceeding or falling below an acceptable range, such as 200 psi maximum and 50 psi minimum, to both protect the well and downstream equipment. (The maximum limit does not prevent the previously-described "off the chart" giveaway situation from occurring.) If any of the prior art proportioning valves currently available on the market were incorporated into the high-low controller, that would effectively double its cost. This would not be acceptable to well producers. Furthermore, there is insufficient extra electrical power available from the photovoltaic cells and batteries used to operate the high-low controller to meet the energy demand of such a high power-consuming proportioning valve.
Consequently, a need remains for an improved proportioning valve system which provides a solution to the aforementioned problems with prior art proportioning values without introducing any new problems in place thereof.